We were east bound and down, headed toward Pueblo, and getting to know the Jeep. We notice, that we were headed for rain. I asked Brian if he checked the wipers, "nope, did you?" Of course I didn't and we'd just left an O'Reilly's.
We got lucky, and actually had half decent wiper blades.
We were in the mountains now, thin air, 35" tires, and the 4 cylinder, we found ourselves making a long line of "friends" behind us, and really testing out 3rd gear that the seller had warned us about.
The Jeep was unnerving at first, with the 4 link, short wheel base, and no sway bars, we were fighting the rear locker every time we let off the throttle. We got used to it, but the first 100+ miles, especially in the rain, and mountain road, there was a real pucker factor every time you let off throttle and the Jeep would try and snap to the right.
We spent a lot of time in 3rd gear climbing those hills, and we notice a roaring grinding noise when coasting down hill, or applying light throttle, down hill. The first few times we heard the noise, I thought "great, we're going to lose 3rd before we're even half way to Pueblo."
Brian and I aren't master mechanics, but we were both farm boys, Brian still is, we know a thing or two, and have a lot of experience in Jeeps. The more we heard the noise, the more we were sure it wasn't the transmission. We'd both decided that the noise was coming from the rear end. The seller had assured us that he'd topped off all the fluids, and snugged all the nuts/bolts, but the only fluids we'd actually checked were oil and coolant before we left.
We pulled off at the next opportunity we had. Maybe there isn't any gear oil in the rear axle? Maybe it's leaked out since the seller claimed to have topped it off?
Brian broke open his new Harbor Freight tool kit, and pulled the rear diff plug.
The diff is full of fluid, weird?
We got back on the road, really paying close attention to the rear end noise, and under what conditions it occurred. We came to the conclusion that either the teeth, or more likely the die springs, in the locker are worn out. The locker is slipping when coasting down hill, and grinding.
We briefly considered hunting down a set of spider gears, or even going up to 4 Wheel Parts in Colorado Springs in search of a spring kit for the locker, but with some practice, modulating the throttle, we mostly learned how to drive around the issue, and soldiered on.
Brian even got the Jeep to do more than 65, with a little help from gravity.